1. Field of the Invention
The invention relates to a fuel injection device that is applied to an internal combustion engine equipped with a supercharger to execute post-injection from a fuel injection valve during the expansion stroke or the exhaust stroke separately from the fuel injection executed for torque generation, and to a control method for the fuel injection device.
2. Description of the Related Art
Internal combustion engines equipped with superchargers for forcing air into the combustion chambers are disclosed (see Japanese Patent Application Publication No. 4-191452 (JP-A-4-191452) and Japanese Patent Application Publication No. 2-218921 (JP-A-2-218921)). In a type of internal combustion engine that directly injects fuel into its combustion chamber, an amount of fuel appropriate to the state of operation of the engine is supplied by controlling the opening and closing of the fuel injection valve in accordance with the state of operation.
Furthermore, in internal combustion engines, an exhaust purification device that includes a catalytic converter, an exhaust filter, etc., for purifying exhaust gas is provided on an exhaust passageway. In order to obtain full performance of the function of the exhaust purification device, post-injection is executed. This post-injection is a fuel injection from a fuel injection valve that is executed during the expansion stroke or the exhaust stroke, and is executed separately from the fuel injection executed for torque generation.
Still further, internal combustion engines are equipped with a sensor for detecting the amount of air flowing in an intake passageway (e.g., an intake air amount sensor, a pressure sensor, etc.). On the basis of the air amount (passageway air amount) detected by the sensor, various controls concerning the operation of the internal combustion engine (e.g., the fuel injection valve opening-closing control, or the like) are executed.
In the supercharger-equipped internal combustion engine, the passageway air amount rapidly increases at the time of sharp acceleration. At this time, a part of the increase in the passageway air amount is consumed by the rise in the intake pressure. Therefore, during a period until the air pressure in the intake passageway (intake air pressure) rises to a pressure appropriate to the engine operation state, the degree of increase in the amount of air actually taken into the combustion chamber (in-cylinder air amount) is smaller than the degree of increase in the aforementioned passageway air amount, and therefore a deviation occurs between the passageway air amount and the in-cylinder air amount.
If the engine control is executed without taking this deviation into account, the engine control is executed in a fashion that accords not with the in-cylinder air amount, which is comparatively slow in increase, but with the passageway air amount, which is greater in the degree of increase than the in-cylinder air amount. Therefore, for example, if an amount of air in accordance with the passageway air amount is injected from the fuel injection valve, an unnecessarily large amount of fuel is supplied into the internal combustion engine, and the air-fuel ratio (=air amount/fuel amount) in the combustion chamber becomes an unnecessarily fuel-rich ratio.
Furthermore, if the post-injection is executed during sharp acceleration, excessive increase in the amount of unburned fuel components in exhaust gas will likely result since the sharp acceleration itself is an operation state in which the air-fuel ratio in the combustion chamber tends to be a fuel-rich side air-fuel ratio, and fuel is added by the post-injection.
If the amount of unburned fuel components in exhaust gas actually becomes excessively large, a part of the amount of unburned fuel components in exhaust gas passes unreacted through the exhaust purification device, and is emitted out of the exhaust passage, and thus the property of emissions deteriorates; for example, white smoke is produced, or the like.